INFLUENCE OF SOIL CONDITIONS 87 



2CH3-CHO + H2O = CH3CH2OH + CH3COOH 



Acetaldehyde Ethyl alcohol Acetic acid 



2CH3CH2OH = CH3COOH + 2CH4 



Ethyl alcohol Acetic acid Methane 



2CH3-CHOHCOOH = CH3 • CH2 • CH2 • COOH -^ 2CO2 + 2H2 



Lactic acid Butyric acid 



Various bacteria are capable of decomposing cellulose in the 

 absence of atmospheric oxygen if nitrate is present; under such 

 conditions the nitrate is used as a source of oxygen. The nitrate 

 is reduced to gaseous nitrogen, and the oxygen thus liberated is 

 used for the decomposition of the cellulose. 



A number of actinomyces decompose cellulose but at a com- 

 paratively slow rate. The nature of the reaction is still unknown. 



Influence of Soil Conditions upon Cellulose Decompo- 

 sition. — The above considerations tend to explain why cellulose is 

 decomposed in different soils with different degrees of rapidity. 

 The soil conditions, such as moisture, reaction, aeration, organic 

 matter content, and supply of available nutrients, influence the 

 types of organisms present in the soil and the types that take an 

 active part in the decomposition of the cellulose; these organisms 

 in their turn influence the nature of the chemical reactions brought 

 about and the nature of the products formed. However, the 

 microbes which have the capacity of decomposing cellulose are so 

 numerous in the soil, they are of such various forms, and they 

 differ so greatly in physiological requirements, that, wherever 

 sufficient inorganic nutrients are available and wherever there is 

 adequate moisture and the temperature conditions are favorable, 

 cellulose is rather quickly decomposed. Either under moderate or 

 excessive moisture, at acid, neutral, or basic reactions, at moderate 

 or high temperatures, some microbes will find conditions conducive 

 to their activity. However, the mechanism of the decomposition 

 and the chemistry of the products formed will be different. The 

 formation of organic substances through the synthesizing agencies 

 of microorganisms contributes one of the sources of the soil organic 

 matter frequently referred to as soil humus. 



Fig. 45 shows the comparative growth of the three major groups 

 of microorganisms, namely the bacteria, fungi, and actinomyces, 

 during the decomposition of cellulose at different moisture 

 contents. 



